International Business Machines Corporation

John F Sweeney

Michael Anthony Sorna

James R Mallabar

Thomas J Smith

A circuit and method for digitizing jitter in a high speed digital signal receives a digital signal using a comparator and supplies a clock signal to a counter. The circuit and method determine the frequency of the digital signal using the clock signal and the counter, and calculate the period of the digital signal based on the frequency (using a logic element). The method and circuit provide a linearized delay for jitter analysis based on the period of the digital signal (using a delay shift circuit) and output a delayed digital signal from the digital signal based on the linearized delay (using a measure delay circuit). The circuit and method supply the digital signal and the delayed digital signal to a programmable unit. The programmable unit comprises flip flops. The circuit and method count transitions of the flip flops within the programmable unit using the counter. The flip flops transition when the digital signal differs from the delayed digital signal. The circuit and method repeat the counting of the transitions of the flip flops for different time intervals to generate a jitter histogram of the digital signal using the logic element.

Jitter digitizer

An apparatus is provided for measuring an output of a high-speed data transmission circuit. The apparatus includes a programmable reference voltage generator operable to generate a reference voltage that is variable between a plurality of levels. The apparatus also includes a quantizer to quantize an output of the high-speed data transmission circuit relative to the reference voltage level input thereto. Also included is a clock generator operable to generate a clock having a transitioning time (rise-time, fall-time or both) that is less than one quarter of a minimum switching period of the output of the circuit. Finally, the apparatus includes a sampler operable to sample the quantized output with the clock to produce a plurality of samples which measure the output of the circuit.

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Colchester, VT, United States of America

John F Sweeney